The intent of this proposal is to study the role of insoluble glucan synthesized by Streptococcus mutans from sucrose in modifying the demineralizing potential of dental plaque. An intraoral enamel demineralization test (IEDT) recently developed by Brudevold et al. (1984), which relies on changes in the iodide permeability of bovine enamel as a measure of enamel demineralization, will be used to evaluate the virulence of five test strains. Artificial plaques will be prepared for testing in the IEDT by sedimentation of test strain cultures. Other bacterial characteristics, namely ability to colonize the tooth surface, produce sufficient acid to cause enamel demineralization, and synthesize intracellular polysaccharides (IPS), have also been associated with virulence. These traits can all be expressed at the same time making it difficult to study one specific trait. The identification and characterization of mutant strains defective in specific virulence traits have greatly improved our ability to study bacterial virulence. A main objective will be to isolate the effect of insoluble glucan from these other virulence traits. This will be accomplished by: 1. evaluating five test strains selected for their virulence or lack of a specific virulence trait with IEDT. 2. comparing the demineralizing potential of the five test strains with their acidogenicity/aciduricity as determined by in situ pH measurements. 3. measuring the demineralizing potential of the five test strains grown under conditions conducive to the synthesis of high or low levels of IPS. 4. measuring the demineralizing potential of five test strains grown under conditions which will yield artificial plaques with varying amounts of insoluble glucan. 5. measuring the demineralizing potential of artificial plaques formed by mixing glucan free cells with fixed ratios of insoluble glucan. The proposed research should provide information on fundamental aspects of caries etiology as well as have relevance to preventive strategies such as immunization directed against glucosyltransferase and bacterial replacement therapy with avirulent mutants.